1. Field of the invention
The present invention relates to a vehicle in which an engine is automatically stopped when predetermined engine stop conditions are met and restarted when predetermined restart conditions are met, and more particularly to a control device of the vehicle for restarting the engine by engaging a predetermined clutch of an automatic transmission upon restarting.
2. Description of the Related Art
For example, as a related art, Japanese Patent Application Laid-Open No. HEI8-193531 discloses a vehicle wherein if the vehicle stops running and predetermined engine stop conditions are met, an engine is stopped automatically so as to save fuel, reduce exhaust emission, attenuate noise or the like. In such a vehicle, if predetermined engine restart conditions are met when a driver shows the intention of driving the vehicle by depressing an accelerator pedal, the engine is restarted immediately.
In a vehicle in which a hydraulic automatic transmission is installed, if an engine is stopped, an oil pump coupled to the engine is also stopped. For this reason, for example, oil that has been supplied to a forward clutch of the automatic transmission leaks out from an oil passage, thereby causing a drop in hydraulic pressure. Therefore, in restarting the engine, the forward clutch, which should be engaged during a forward running state of the vehicle, is still disengaged. In such case, unless the forward clutch is promptly engaged when the engine is restarted, the accelerator pedal is depressed, as it were, in a neutral state. Therefore, the forward clutch is engaged when the engine is at a high engine speed, whereby an engagement shock is caused. As a result, the amount of work done by the clutch increases, which may adversely affect the durability of the clutch.
Accordingly, in order to prevent such condition, a technique is proposed by the aforementioned Japanese Patent Laid-Open No. HEI 8-14076 wherein a large-sized accumulator functions to maintain the forward clutch in an engaged state until the engine which has been automatically stopped is restarted. Further, Japanese Patent Laid-Open No. HEI 9-39613 discloses a technique in which, rather than stopping the engine operation completely, the fuel supply to the engine is stopped but the engine speed is kept at an idle speed by a motor generator, such that the operation of the oil pump is not stopped.
However, the technique disclosed in Japanese Patent Laid-Open No. HEI 8-14076 in which the forward clutch is kept in an engaged state with a large-sized accumulator when the engine is stopped could not eliminate other disadvantage due to the accumulator, such as deterioration of a drain performance during shifting from a D (drive) position to an N (neutral) position, that is, retarding of the releasing speed of the forward clutch, or enlarging of the hydraulic control device, for example. Further, the technique disclosed in Japanese Patent Laid-Open No. HEI 9-39613, wherein the engine is maintained at an idle speed by a motor generator is able to reduce the fuel consumption. However, it demands a larger battery (larger capacity) because driving by the motor generator involves significant battery consumption.